Secondary oil recovery

ABSTRACT

Improving secondary recovery following breakthrough of driving fluid at the production wells of inverted five-spot patterns by reversing the functions of injection wells in alternate patterns to producing and that of production wells to injecting.

United States Patent 1191 Haynes, Jr.

1 1 Apr. 23, 1974 1 1 SECONDARY OIL RECOVERY [75] Inventor:

[73], Assignee: Texaco Inc., New York, NY.

Stewart Haynes, Jr., Houston, Tex.

3,143,169 8/1964 Foulks 166/245 3,113,618 12/1963 Oakes 166/245 3,253,652 5/1966 Connally et a1 166/245 3,380,525 4/1968 Altamira et al..... 166/245 3,270,809 9/1966 Connally et a1 166/263 3,402,768 9/1968 Felsenthal et a1... 166/245 3,429,372 2/1969 Connally 166/245 Primary Examiner-Ernest R. Purser Assistant Examiner-Jack E. Ebel Attorney, Agent, or Firm-T. Whaley; C. G. Ries 57] ABSTRACT Improving secondary recovery following breakthrough of driving fluid at the production wells of inverted five-spot patterns by reversing the functions of injection wells in alternate patterns to producing and that of production wells to injecting. Y

4 Claims, 6 Drawing Figures pfiaaz/cr/a/y 14 2 21 ,6 'mffaf/d/v 14 222 6 ma/wa/wew/vg W221 J'Y'MENTEDAPR 23 1914 SHEET 1 BF 2 Fig.1.

' x fiacr/o/v 14 1521 ,0 //Vft2770/V W424 K II I f I Av K w m 0 0M W W l w 4 w w (a, l A A K W! m 1 1 Aw T m Tull PATENTEDAPR 23 mm 3805:8532 SHEET 2 [IF 2 SECONDARY on. RECOVERY FIELD OF THE INVENTION DESCRIPTION OF THE INVENTION In the production of hydrocarbons from permeable subterranean hydrocarbon-bearing formations, it is customary to drill one or more boreholes or wells into the hydrocarbon-bearing formation and produce formation fluids including hydrocarbons, such as oil, through designated production wells, either by the natural formation pressure or by pumping the wells. Sooner or later, the flow of hydrocarbon-bearing fluids diminishes and/or ceases, even though substantial quantities of hydrocarbons are still present in the underground formations.

Thus, secondary recovery programs are now an essential part of the overall planning for exploitation of oil and gas-condensate reservoirs in subterranean hydrocarbon-bearing formations. In general, this involves injecting an extraneous fluid, such as water or gas, into the reservoir zone to drive formation fluids including hydrocarbons toward production wells by the process commonly referred to as flooding. Usually, this flooding is accomplished by injecting through wells drilled in a pattern, e.g. the alternating line drive and the more commonly used five-spot pattern, which may be visualized as a special type of staggered line drive pattern wherein the separation of the lines of wells is half the spacing between the individual wells.

When the driving fluid, e.g. water, from the central injection well reaches the corner production wells of an inverted five-spot pattern, the areal sweep efficiency is about 71 percent. By continuing production considerably past breakthrough, it is possible to produce more of the remaining unswept portion although continued injection will not reduce oil saturation much further.

SUMMARY OF THE INVENTION It is an overall object of the present invention to provide an improved recovery procedure involving a series of inverted five-spot well pattern arrangements for exploiting a hydrocarbon-bearing formation, by changing the functions of production wells and selected injection wells in the patterns at determined intervals.

A series of inverted five-spot patterns is arranged in a producing field so that the central well of each pattern is completed for injection and the corner wells are completed for production. Flooding is initiated at the central well by injection thereinto of a driving fluid, such as water, and proceeds until breakthrough of the flood front occurs at the corner production wells, at which time, these are placed on a stand-by basis and injection via the central well may be suspended or terminated. Then, the function of the injection wells of alternate patterns is changed to a production basis, and driving fluid is injected via the remainder of the injection wells to drive formation fluids toward the newly designated production wells. Upon breakthrough of formation fluid thereat, injection thereof is initiated at the original production wells, now on a stand-by basis, and terminated at the original injection wells, and production is maintained at the wells converted to production.

Other objects, advantages and features of this invention will become apparent from a consideration of the specification with reference to the figures of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 discloses the symbols used in the remaining figures of the drawing;

F Ig. 2 is a representation of an inverted five-spot pattern producing field undergoing a recovery procedure at the time of driving fluid breakthrough at the corner production wells;

FIG. 3 represents the same field at a later phase of the recovery procedure, following the changes of functions of certain wells in the five-spot patterns;

FIG. 4 represents a still later phase of the recovery procedure, at breakthrough of formation fluids at the converted production wells of the five-spot patterns and the start of injection at the original production wells;

FIG. 5a represents an ending stage of the phase of FIG. 4, depicting the advance of driving fluid and formation fluids; and

FIG. 5b is a representation of the producing field at the final phase of the recovery procedure.

The objects of the invention are achieved by changing the functions of the wells in an inverted five-spot pattern arrangement to provide an advantageous drive of regions of high oil saturation toward newly chosen production wells during a recovery procedure.

The specification and the figures of the drawings schematically disclose and illustrate the practice and the advantages of the invention with an inverted fivespot well pattern which may be observed in potentiometric model studies which simulate recovery operations. The model studies indicate a sweep-out obtained in an ideal reservoir, although the recovery from an actual sweep-out of a particular field may be greater or less, depending on field parameters.

Throughout the figures of the drawings, the same symbols will be maintained as disclosed in FIG. 1, viz. a solid circle indicates a production well, an open circle with a first quadrant arrow indicates original injection well, and a crossed open circle, an original production well on a stand-by basis.

Referring to FIG. 2, there is represented symbolically breakthrough at the corner production wells of a series of inverted five-spot patterns in a producing field in a secondary recovery procedure, wherein recovery of about 7l percent sweep-out efficiency is achieved. (A mobility ratio of 1.0 is assumed for water flooding). It is postulated that about 28 percent of the recoverable hydrocarbons in the formation remain unswept. It is recognized that additional amounts of hydrocarbons may be recovered with injection and production continued after breakthrough of the driving fluid.

Then, the original production wells are put on a stand-by basis and the injection wells of alternate patterns are converted to production wells, as represented in FIG. 3. As driving fluid is injected into the formation via the remaining injection wells, the roughly annular shape of the cusps of remaining hydrocarbons (oil bank), as shown in FIG. 2, assume the configurations of FIG. 3, as production continues via the converted original central injection wells. Driving fluid, such as water, produced from such new recovery wells, can be used for injection via the companion injection wells.

In FIG. 4, an enlarged showing of a unit of an inverted five-spot pattern in a recovery operation following breakthrough of formation fluids at the new production well, with the stand-by original corner production wells converted to injection wells, the injection being at a controlled rate.

FIG. 5 also is an enlarged showing of a unit of an inverted five-spot pattern, depicting the closing advance of the formation fluids and the driving fluid at a phase later than that shown in FIG. 4, indicating an easy sweep-out of the fluids adjacent the production well; and FIG. 5b is a general representation of the formation fluids in the producing field at the end of the recovery operation.

Thus, there has been shown and described the manner by which a recovery operation involving inverted five-spot patterns may be improved considerably following the breakthrough ofa driving fluid at the corner production wells, by reversing the functions of certain central injection wells to production wells, and that of the corner production wells to injection wells, as comparison of the remaining formation fluids in FIGS. 2 and 5 will indicate.

As will be apparent to those skilled in the art in the light of the accompanying disclosure, other changes and alterations are possible in the practice of this invention without departing from the spirit or scope thereof.

I claim:

1. A method of producing formation fluids including hydrocarbons from a subterranean hydrocarbonbearing formation which comprises penetrating. said formation with a plurality of wells, said wells defining a series of inverted five-spot patterns, injecting an extraneous fluid into said formation via the injection wells of each of said patterns to displace formation fluids including hydrocarbons therefrom toward the production wells of said patterns, producing said formation fluids including hydrocarbons from said formation via said production wells and ceasing producing said formation fluids via said production wells upon breakthrough of said extraneous fluid thereat, and thereupon converting injection wells of alternate patterns to production wells and producing therefrom while injecting said extraneous fluid via the unconverted injection wells until breakthrough of said formation fluids at the converted injection wells, thereafter injecting said extraneous fluid into said formation via the original production wells and producing said formation fluids via the converted injection wells.

2. In the method as defined in claim 1, closing in the production wells upon breakthrough of said extraneous fluid thereat.

3. In the method as defined in claim 1, upon breakthrough of said formation fluids at the converted injection wells, initiating injecting said extraneous fluid into said formation via the original production wells at a controlled rate.

4. In the method as defined in claim 3, ceasing injecting said extraneous fluid into said formation via the unconverted injection wells after a period of time following initiating injecting via the original production wells. 

1. A method of producing formation fluids including hydrocarbons from a subterranean hydrocarbon-bearing formation which comprises penetrating said formation with a plurality of wells, said wells defining a series of inverted five-spot patterns, injecting an extraneous fluid into said formation via the injection wells of each of said patterns to displace formation fluids including hydrocarbons therefrom toward the production wells of said patterns, producing said formation fluids including hydrocarbons from said formation via said production wells and ceasing producing said formation fluids via said production wells upon breakthrough of said extraneous fluid thereat, and thereupon converting injection wells of alternate patterns to production wells and producing therefrom while injecting said extraneous fluid via the unconverted injection wells until breakthrough of said formation fluids at the converted injection wells, thereafter injecting said extraneous fluid into said formation via the original production wells and producing said formation fluids via the converted injection wells.
 2. In the method as defined in claim 1, closing in the production wells upon breakthrough of said extraneous fluid thereat.
 3. In the method as defined in claim 1, upon breakthrough of said formation fluids at the converted injection wells, initiating injecting said extraneous fluid into said formation via the original production wells at a controlled rate.
 4. In the method as defined in claim 3, ceasing injecting said extraneous fluid into said formation via the unconverted injection wells after a period of time following initiating injecting via the original production wells. 